While undergoing now booming development in the analytical field, the SFC technique on preparative scale is however, for the time being, much less established.
Therefore, many natural products are recovered through the employment of more traditional technologies. Among the recovery of natural products, in particular of those employed for pharmaceutical purposes, a particular field of interest is the separation of fatty acids, preferably unsaturated, in particular polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from marine oils, in particular from fish oils. Aforementioned fatty acids are referred to as “omega-3 fatty acids” (more exactly: C20:5 ω-3 and C22:6 ω-3), and the positive health effect brought about by their consumption has been extensively reported in the last 20-25 years.
Since most naturally occurring marine oils are not particularly concentrated in omega-3 fatty acids and since untreated fish oils of medium omega-3 fatty acid content inherently have an unsavory fish odour and flavour, a number of processes have been developed in the last years for refining the crude oils and for separating the omega-3 fractions, such as to provide highly purified preparations employable for pharmaceutical purposes. This is because the employment of lower concentrated preparations is excised by the Pharmacopeia, such that the same can only be exploited as food supplements, not as pharmaceuticals.
Various purification techniques, including urea complexing, adsorption, HPLC, Super critical fluid extraction, fractional and/or molecular distillation etc., have therefore been applied alone or in combination, to purify the omega-3 fractions from marine oils. An example of such previous techniques is given in William B. Nilsson et al. “Supercritical Fluid Fractionation of Fish Oil Esters using Incremental Pressure Programming and a Temperature Gradient.” JAOCS, Vol. 66, no. 11 (November 1989). Supercritical fluid fractionation as relied upon by Nilsson et al. is a distillation technique involving the use of a vertical column having an internal structure or packing made of an inert material providing for an increased surface, such as to ease the achievement of an equilibrium between the fluid phases involved. The inert packing material (e.g. Sulzer® packings, Raschig® rings, ball bearings etc.) has an exclusively geometrical function and does not take part, as such, in the phase equilibrium.
However, most of these conventional techniques are cumbersome and time consuming, especially, if they are employed to arrive at highly purified (75% or more) EPA and/or DHA preparations. The use of these methods is therefore mainly indicated for the attainment of pre-purified (or pre-refined) mixtures of fatty acids or of their derivatives, most advantageously of their ethyl esters, to be subjected then to a more efficient final downstream step of improved selectivity.
Therefore, the substrates nowadays employed in the said last refining steps for the manufacture of omega-3 fatty acid based pharmaceuticals are normally pre-enriched ethyl ester compositions derived from marine materials being lower that 75% in EPA and/or DHA.
Among the most recent technological attempts to achieve the final purification with modern separation methods employing supercritical fluids is U.S. Pat. No. 5,719,302 to Perrut et al. who describes, in an attempt to overcome the low productivity achieved heretofore with large scale stationary bed HPLC employed earlier in the art, a process for chromatographic fractionation of fatty acids and their derivatives, such process comprising, in one of its steps, subjection of a feed composition to simulated continuous countercurrent moving bed chromatography with supercritical CO2 as eluent, with the aim of recovering fractions of purified polyunsaturated fatty acids.
However, costs for the construction of a plant of the type used by U.S. Pat. No. 5,719,302 are high, and reduction to practice of the method described therein, in particular the fine tuning of the process parameters, is difficult, such that, to Applicant's knowledge, no preparations obtained with this method have, so far, actually hit the market.
On top of the aforementioned method, some years ago, a mixed preparative SFC/SFE technique “on column” for recovering a substance or a group of substances from a mixture has been proposed, for the first time, by the Applicant of the present invention in order to increase the throughput of batchwise SFC separation, see EP 712 651. SFC/SFE is particularly suited for the separation of fatty acid mixtures and of mixtures of their ethylesters, be the same pre-refined (i.e. pre-enriched) as indicated above, or not. The batchwise mixed preparative SFC/SFE technique can be easily adopted by overloading the employed SFC column in a controlled manner and is operated with success by the Applicant who has a long-grown experience in the field.
However, due to the strongly increasing demand for highly purified products, a continued need of improved, highly preferment separation methods, and as well as of the products thereby obtained, still exists.
It hence appears that there is a problem in the art, calling for the provision of a still improved process, for recovering a substance or a group of substances from a mixture with improved efficiency. The improved process should be able to provide equally pure products as the ones known in less time or in greater amounts, preferably with the possibility to provide, contemporaneously, still more purified products.